linux-kernel - Re: [PATCH v3 1/8] sched, x86: Add SD_ASYM_PACKING flags to x86 cpu topology for ITMT

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Date:   Sat, 10 Sep 2016 15:10:43 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
cc:     rjw@...ysocki.net, mingo@...hat.com, bp@...e.de, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, peterz@...radead.org,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH v3 1/8] sched, x86: Add SD_ASYM_PACKING flags to x86 cpu
 topology for ITMT

On Thu, 8 Sep 2016, Srinivas Pandruvada wrote:
> From: Tim Chen <tim.c.chen@...ux.intel.com>
> 
> We uses ASYM_PACKING feature in the scheduler to move tasks to more
> capable cpus that can be boosted to higher frequency. This is enabled by
> Intel Turbo Boost Max Technology 3.0 (ITMT).  We mark the sched domain
> topology level with SD_ASYM_PACKING flag for such systems to indicate
> scheduler can use the ASYM_PACKING feature to move load to the
> more capable cpus.

Sigh. This changelog does not tell anything about the nature of the patch,
the rationale for it etc. It's just a meaningless blurb.


> +unsigned int __read_mostly sysctl_sched_itmt_enabled;
> +
>  static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
>  {
>  	unsigned long flags;
> @@ -471,31 +473,57 @@ static bool match_die(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
>  	return false;
>  }
>  
> -static struct sched_domain_topology_level numa_inside_package_topology[] = {
> +#ifdef CONFIG_SCHED_ITMT
> +static int x86_core_flags(void)
> +{
> +	int flags = cpu_core_flags();
> +
> +	if (sysctl_sched_itmt_enabled)
> +		flags |= SD_ASYM_PACKING;
> +
> +	return flags;
> +}
> +
> +static int x86_smt_flags(void)
> +{
> +	int flags = cpu_smt_flags();
> +
> +	if (sysctl_sched_itmt_enabled)
> +		flags |= SD_ASYM_PACKING;
> +
> +	return flags;
> +}
> +#else
> +#define x86_core_flags cpu_core_flags
> +#define x86_smt_flags cpu_smt_flags
> +#endif

No. We first rework the code so that the IMT stuff can be added in a later
patch easily.

Thanks,

	tglx